The present invention relates to a method of treating a tow of filamentary filter material, especially a tow which is about to be converted into the filler of a filter rod adapted to be subdivided into filter rod sections of desired length. Such filter rod sections are used in filter tipping machines for the mass production of filter cigarettes, cigars or cigarillos.
It is well known to apply a liquid plasticizing agent, such as triacetin and hereinafter called plasticizer, to a running tow of filamentary filter material. The plasticizer is atomized so that it forms a myraid of minute droplets which are propelled against the running tow and cause portions of neighboring filaments to become soft and adhere to each other so that the filaments of the filler form a maze of passages for the flow of tobacco smoke into the mouth. As a rule, the tow is first converted into a relatively wide but thin layer wherein all or nearly all of the filaments are exposed during application of plasticizer (note the commonly owned U.S. Pat. No. 3,971,695 granted July 27, 1976 to Block); this ensures more uniform distribution of droplets of plasticizer on the filaments of the tow. The thin layer of filamentary material is at least slightly permeable to liquids, i.e., a certain percentage of minute droplets of plasticizer penetrates through the interstices or gaps between neighboring filaments of the tow and must be gathered for renewed use or for delivery to a location where the thus gathered liquid does not interfere with the application of atomized plasticizer to freshly arriving increments of the running tow. In most instances, the liquid plasticizer is atomized and applied to the running tow at a predetermined rate, namely, in such a way that the quantity of liquid plasticizer which is applied to successive unit lengths of the running tow remains unchanged even if the speed of the tow is increased or reduced. This can be readily accomplished by utilizing a pump which supplies plasticizer to the plasticizer-atomizing and plasticizer-applying station at a speed which changes proportionally with variations in velocity of the running tow. The latter is withdrawn from a bale and is caused to pass along, through or past and beyond one or more so-called banding devices which facilitate conversion of the tow into a layer whose filaments are adjacent to each other and are adequately exposed for proper application of atomized plasticizer. The tow is thereupon gathered into a rod-like filler which is draped into a web of cigarette paper or the like to form therewith a continuous filter rod. The rod is severed at regular intervals to yield filter rod sections of desired length, and such sections are ready to enter the magazine of a filter tipping machine, the storage or a reservoir system wherein the curing of plasticizer is completed and which discharges filter rod sections at a rate at which the sections are processed in one or more associated filter tipping machines.
The filaments of the tow often consist of cellulose, and the plasticizer is selected with a view to soften the contacted portions of such filaments and to cause the softened portions to adhere to each other. This leads to formation of the aforementioned maze of minute passages or paths for the flow of tobacco smoke into the mouth. Many smokers are quite particular as regards the so-called draw of a filter cigarette or another smokers' product having a filter plug at one end thereof. Excessive resistance to the flow of smoke is not desirable because each drag entails the exercise of a substantial effort and the smoker fails to draw sufficient quantities of smoke into his or her mouth. On the other hand, insufficient resistance to the flow of smoke is equally (or perhaps even more) unsatisfactory because the quantity or inhaled smoke is excessive and/or because the smoke is too hot and the filter fails to remove or intercept a requisite percentage of nicotine, condensate and/or other deleterious or presumably deleterious ingredients.
Predictable resistance to the flow of tobacco smoke through a filter involves the application of liquid plasticizer in accurately metered quantities. Such predictable (and evidently acceptable or optimum) resistance is desirable and advantageous on the the additional ground that it is least likely to interfere with proper operation of apparatus, mechanisms and/or machines for further treatment of filter plugs. Thus, filter plugs of excessive hardness would be likely to damage (e.g., puncture) the uniting band material which is used to connect filter plugs with rod-shaped tobacco-containing articles, such as plain cigarettes of unit length or multiple unit length. Excessive application of plasticizer (i.e., the application of excessive quantities of plasticizer per unit length of the two) is undesirable on still another ground, namely, because the plasticizer is expensive and excessive application results in waste of such material as well as in excessive number of rejects, i.e., of finished filter rod sections which are not acceptable for further processing in a filter tipping or like machine.
It is well known to confine the station where the atomized plasticizer is applied to successive increments of the running tow in a housing designed to gather the plasticizer which has penetrated through the interstices between the filaments of the running tow. The droplets of plasticizer which have penetrated through the tow are caused to impinge upon the internal surface of the housing, and such internal surface is configured to direct the gathered liquid into the range of one or more atomizing instrumentalities, e.g., rotary brushes whose bristles convert the liquid into minute droplets while simultaneously propelling the droplets against one or both sides of the running tow. The just described mode of gathering or intercepting atomized plasticizer which has penetrated through or across the running tow is quite satisfactory when the machine for making filter rod sections operates normally, i.e., when the tow is driven at a normal or average speed, when the plasticizer is delivered at a rate which is proportional to the speed of lengthwise movement of the tow, and when the nature of the tow is such that the latter can accept optimum quantities of finely atomized plasticizer. The preferably smooth internal surface of the housing can direct the surplus of plasticizer (and more accurately the plasticizer which has penetrated through the running tow) into the range of a rotary brush in the lower portion of the housing, and such liquid plasticizer returns or flows into the lower portion of the housing by trickling along walls which flank one or both sides of the path for lengthwise movement of the running tow through the housing. After elapse of a certain interval following starting of the machine, the machine establishes in the housing a so-called internal equilibrium which simply means that the quantity of admitted plasticizer machines or very closely approximates that quantity of atomized plasticizer which is evacuated by successive increments of the running tow. The internal equilibrium can be established (or its establishment promoted) by varying the rate of delivery of plasticizer to the atomizing station while the tow is transported at a constant speed.
A drawback of presently known methods and apparatus for applying liquid plasticizer is that the aforediscussed internal equilibrium is invariably destroyed when the filter rod making machine is arrested, and also that it takes a relatively long interval of time to reestablish such equilibrium after renewed starting of one or more prime movers which drive the rotary and/or otherwise movable constituents of the machine. The internal equilibrium is also destroyed or rendered unsatisfactory if the feed of one of two constituents (filter tow and plasticizer) to the atomizing station is changed while the rate of delivery of the other constituent remains unchanged. Since a modern high-speed filter rod making machine turns out very large quantities of rod-shaped articles per unit of time, and since the filter rod sections which contain unsatisfactory quantities of plasticizer must be segregated because they would contribute to the making of unsatisfactory smokers' products, it is evidently desirable to reduce the period of absence of the internal equilibrium to a minimum.